Fast-response micro-mechanical devices

ABSTRACT

A spatial light modulator includes a mirror plate comprising a reflective upper surface, a lower surface, and a substrate portion comprising a cavity having an opening on the lower surface, a substrate comprising an upper surface, a hinge support post in connection with the substrate, and a hinge component supported by the hinge support post and in connection with the mirror plate, and one or more landing tips configured to contact the lower surface of the mirror plate to limit rotation of the mirror plate. The hinge component includes a protrusion that is anchored in a hole in the top surface of the hinge support post and the hinge component is configured to extend into the cavity to facilitate rotation of the mirror plate.

BACKGROUND

The present specification relates to spatial light modulators.

Over the past fifteen to twenty years, micro mirror based spatial lightmodulator (SLM) technology has undergone many incremental technicaladvancements and gained greater acceptance in the display industry. Thedevices operate by tilting individual micro mirror plates in the arrayaround a torsion hinge with an electrostatic torque to deflect theincident light to a predetermined exit direction. In a more populardigital mode operation, the light is turned “on” or “off” by rotatingselectively the individual mirrors in a micro mirror array andmechanically stopped at a specific landing position to ensure theprecision of deflection angles. A functional micro mirror array requireslow contact sticking forces at the mechanical stops and high efficiencyof electrostatic torques to control timing, to overcome surfaces contactadhesions, and to ensure the robotics and reliability. A highperformance spatial light modulator for display application produceshigh brightness and high contrast ratio videos images.

Early SLM in video applications suffered a disadvantage of lowbrightness and low contrast ratio of the projected images. Previous SLMdesign typically has a low active reflection area fill-ratio of pixels(e.g., ratio between active reflective areas and non-active areas ineach pixel). A large inactive area around each pixel in the array of SLMresults to a low optical coupling efficiency and low brightness. Thescattered light from these inactive areas in the array forms diffractionpatterns that adversely impact the contrast of video images. Anothermajor source of the reduced contrast ratio of micro mirror array basedSLM is the diffraction of the scattered light from two straight edges ofeach mirror in the array that are perpendicular to the incidentillumination. In a traditional square shape mirror design, an orthogonalincident light is scattered directly by the perpendicular straightleading and trailing edges of each mirrors in the array during theoperation. The scattered light produces a diffraction pattern and muchof the diffracted light is collected by the projection lenses. Thebright diffraction pattern smears out the high contrast of projectedvideo images.

One type of micro mirror based SLM is the Digital Mirror Device (DMD),developed by Texas Instruments and described by Hornbeck. The mostrecent implementations include a micro mirror plate suspended via arigid vertical support post on top of a yoke plate. The yoke plate isfurther comprised a pair of torsion hinges and two pair of horizontallanding tips above addressing electrodes. The electrostatic forces onthe yoke plate and mirror plate controlled by the voltage potentials onthe addressing electrodes cause the bi-directional rotation of bothplates. The double plate structure is used to provide an approximatelyflat mirror surface that covers the underlying circuitry and hingemechanism, which is one way in order to achieve an acceptable contrastratio.

However, the vertical mirror support post which elevated the mirrorplate above the hinge yoke plate has two negative impacts on thecontrast ratio of the DMD. First, a large dimple (caused by thefabrication of mirror support post) is present at the center of themirror in current designs which causes scattering of the incident lightand reduces optical efficiency. Second, the rotation of double platecauses a horizontal displacement of mirror reflective surfaces along thesurface of DMD, resulting in a horizontal vibration of a micro mirrorduring operation. The horizontal movement of mirrors requires extralarger gaps to be design in between the mirrors in the array, reducingthe active reflection area fill-ratio further. For example, if therotation of mirror on each direction is 12°, every one micron apartbetween the mirror and the yoke resulting a 0.2 microns horizontaldisplacement on each direction. In other words, more than 0.4 micronsextra gap spacing between the adjacent mirrors is required for every onemicron length of mirror support post to accommodate the horizontaldisplacement.

The yoke structure has limited the electrostatic efficiency of thecapacitive coupling between the bottom electrodes and the yoke andmirror. Especially in a landing position, it requires a high voltagepotential bias between the electrodes and the yoke and mirror to enablethe angular cross over transition. Double plate structure scattersincident light which also reduces the contrast ratio of the videoimages.

Another reflective SLM includes an upper optically transmissivesubstrate held above a lower substrate containing addressing circuitry.One or more electrostatically deflectable elements are suspended by twohinge posts from the upper substrate. In operation, individual mirrorsare selectively deflected and serve to spatially modulate light that isincident to, and then reflected back through, the upper transmissivesubstrate. Motion stops may be attached to the reflective deflectableelements so that the mirror does not snap to the bottom controlsubstrate. Instead, the motion stop rests against the upper transmissivesubstrate thus limiting the deflection angle of the reflectivedeflectable elements.

In such top hanging mirror design, the mirror hanging posts andmechanical stops are all exposed to the light of illumination, whichreduces the active reflection area fill-ratio and optical efficiency,and increase the light scattering. It is also difficult to control thesmoothness of reflective mirror surfaces, which is sandwiched betweenthe deposited aluminum film and LPCVD silicon nitride layers. Depositionfilm quality determines the roughness of reflective aluminum surfaces.No post-polishing can be done to correct the mirror roughness.

SUMMARY

In one aspect, the present invention relates to a spatial lightmodulator, including a mirror plate comprising a reflective uppersurface, a lower surface, and a substrate portion comprising a cavityhaving an opening on the lower surface; a substrate comprising an uppersurface, a hinge support post in connection with the substrate, and ahinge component supported by the hinge support post and in connectionwith the mirror plate, wherein the hinge component includes a protrusionthat is anchored in a hole in the top surface of the hinge support postand the hinge component is configured to extend into the cavity tofacilitate rotation of the mirror plate; and one or more landing tipsconfigured to contact the lower surface of the mirror plate to limitrotation of the mirror plate.

In another aspect, the present invention relates to a spatial lightmodulator, including a mirror plate comprising a reflective uppersurface, a lower surface, and a substrate portion comprising a cavityhaving openings on the lower surface; a substrate comprising an uppersurface, a hinge support post in connection with the upper surface, anda hinge components supported by the hinge support post and in connectionwith the mirror plate, wherein the hinge component is configured toextend into the cavity to facilitate a rotation of the mirror plate; andone or more landing tips anchored into the upper surface of thesubstrate, configured to contact the lower surface of the mirror plateto limit the rotation of the mirror plate.

In yet another aspect, the present invention relates to a spatial lightmodulator, including: a mirror plate comprising a reflective uppersurface, a lower surface having a conductive surface portion, and asubstrate portion comprising one or more cavities having openings on thelower surface; a control substrate comprising an upper surface, one ormore electrodes over the upper surface, one or more hinge support postin connection with the upper surface, and one or more hinge componentseach supported by one of the hinge support posts, wherein at least oneof the hinge components includes a protrusion that is anchored in a holein the top surface of the hinge support post and the hinge component isconfigured to extend into one of the cavities to facilitate a rotationof the mirror plate when an electric voltage is applied across one ofthe electrodes over the control substrate and the conductive surfaceportion in the lower surface of the mirror plate; and one or morelanding tips anchored into the upper surface of the control substrate,configured to contact the lower surface of the mirror plate to limit therotation of the mirror plate.

In another aspect, the present invention relates to a method forfabricating a landing tip for stopping the rotation of a mirror platehinged to a hinge support post in connection with a substrate, includingforming a hole in the upper surface of the substrate; depositing a layerof material over the upper surface of the substrate and in the hole ofthe substrate, wherein the lower portion of the landing tip is to beformed by the material deposited in the hole; and selectively removingthe deposited material over the substrate to form the upper portion ofthe landing tip.

In another aspect, the present invention relates to a method forfabricating a hinge component in connection with a mirror plate and ahinge support post to facilitate the rotation of the mirror platerelative to the hinge support post, including forming a hole in the topsurface of the hinge support post; depositing a layer of material overthe top surface of the hinge support post and in the hole in the topsurface of the hinge support post; and selectively removing thedeposited material over the substrate to form the hinge component havingthe protrusion anchored in the hole in the top surface of the hingesupport post.

In still another aspect, the present invention relates to a method forfabricating a hinge support post in connection with a mirror plate and asubstrate to facilitate the rotation of the mirror plate relative to thesubstrate, including forming a hole in the upper surface of thesubstrate; depositing a layer of material over the upper surface of thesubstrate and in the hole of the substrate, wherein the lower portion ofthe landing tip is to be formed by the material deposited in the hole;and selectively removing the deposited material over the substrate toform the upper portion of the hinge support post.

Implementations of the system may include one or more of the following.At least one of the landing tips can be anchored into the upper surfaceof the substrate. The protrusion and the hinge component can comprise aunitary body. The hinge support post can be substantially upright. Thehinge support post can be anchored into the upper surface of thesubstrate. The one or more landing tips or one or more of the hingesupport posts can comprise a material selected from the group consistingof aluminum, silicon, amorphous silicon, and an aluminum-silicon alloy.The cavity in the substrate portion of the mirror plate and theassociated hinge component can be so configured such that a gap isformed between the hinge component and the surfaces in the cavity topermit the rotation of the mirror plate. The hinge support post over theupper surface can be substantially upright relative to the substrate.

Implementations of the system may include one or more of the following.The hinge component can include a protrusion that is anchored in a holein the top surface of the hinge support post. The hinge support post canbe anchored into the upper surface of the substrate. At least one of thelanding tips can include a lower portion anchored in the upper surfaceof the substrate and an upper portion above the substrate. The lowerportion of the at least one of the landing tips can include a taperedshape anchored in the upper surface of the substrate. The lower portionof the at least one of the landing tips can have substantially the samewidth as the upper portion of the landing tip. The substrate can includea hinge support layer into which the landing tip is anchored. The topsurface of the landing tip can be substantially flat. The one or morelanding tips can be configured to stop the rotation of the mirror platewhen the mirror plate is rotated to one or more predeterminedorientations. The one or more landing tips can be substantially uprightwhen the landing tips are not in contact with the lower surface of themirror plate.

Embodiments may include one or more of the following advantages. Thedisclosed system and methods provide a spatial light modulator (SLM)having a high active reflection area fill-ratio. A pair of torsionhinges extends into the cavities to be part of the lower portion of amirror plate, and are kept in a minimum distance under the reflectivesurface to allow only a gap for a predetermined angular rotation. Themirror plate in the array is suspended by a pair of torsion hingessupported by two posts to allow the mirror plate rotate along an axis inthe mirror plane. By eliminating the horizontal displacement ofindividual mirror during the cross over transition, the gaps betweenadjacent mirrors in the array are significantly reduced, which resultsin a very high active reflection area fill-ratio of the SLM.

The disclosed system and methods provide ways to preventmirror-substrate adhesion and increase the response time of themicro-mirrors. A pair of vertical landing tips is fabricated on thesurface of control substrate. These vertical landing tips reduce thecontact area of mirrors during the mechanical stops, and improve thereliability of mechanical landing operation. Most importantly, theselanding tips enable a mirror landing separation by applying a sharpbipolar pulsing voltage on a common bias of mirror array. The kineticenergy of the electromechanical shock generated by bipolar pulsing isconverted into the elastic strain energy stored in the deformed mirrorhinges and deformed landing tips, and released later on to spring andbounce the mirror separating from the landing tips.

The disclosed system and methods provide a robust spatial lightmodulator. The hinge support posts and the landing tips can be anchoredin the substrate to enhance their mechanical strength and connection tothe substrate. The torsional hinge can also anchored into the topsurface of the hinge support post by a protrusion on the lower surfaceof the torsion hinge. These features strengthen the mechanical stresspoints in the micro mirrors, which significantly increase the durabilityand reliability of the SLM.

The disclosed system and methods are compatible with a wide range ofapplications, such as video displays and printings, display, printing,photo patterning in maskless photolithography, and photonic switches fordirecting optical signals among different optical fiber channels.

Although the invention has been particularly shown and described withreference to multiple embodiments, it will be understood by personsskilled in the relevant art that various changes in form and details canbe made therein without departing from the spirit and scope of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a illustrates a cross section view of a part of the spatial lightmodulator according to one embodiment of the present inventiondeflecting illumination to an “on” state.

FIG. 1 b illustrates a cross section view of a part of the spatial lightmodulator according to one embodiment of the present inventiondeflecting illumination to an “off” state.

FIG. 2 is a perspective view showing the top of a part of the arrays ofrectangular shape mirrors for a projection system with diagonalillumination configuration.

FIG. 3 is a perspective view showing the top of a part of the controlcircuitry substrate for a projection system with diagonal illuminationconfiguration.

FIG. 4 is a perspective view showing the top of a part of the mirrorarray with each mirror having a series of curvature shapes leading andtrailing edges for a projection system with orthogonal illuminationconfiguration.

FIG. 5 is a perspective view showing the top of a part of the controlcircuitry substrate for a projection system with orthogonal illuminationconfiguration.

FIG. 6 is an enlarged backside view of a part of the mirror array witheach mirror having a series of curvature shapes leading and trailingedges for a projection system with orthogonal illuminationconfiguration.

FIG. 7 is a perspective view showing the torsion hinges and theirsupport posts under the cavities in the lower portion of a mirror plate.

FIG. 8 is a diagram illustrates a minimum air gap spacing around thetorsion hinge of a mirror plate when rotated 15° in one direction.

FIG. 9 is a manufacturing process flow diagram for a high contrastspatial light modulator.

FIGS. 10-13 are cross section side views of a part of a spatial lightmodulator illustrating one method for fabricating a plurality of supportframes and the first level electrodes connected to the memory cells inthe addressing circuitry.

FIGS. 14-17 are cross section side views of a part of a spatial lightmodulator illustrating one method for fabricating a plurality of supportposts, second level electrodes, and landing tips on the surface ofcontrol substrate.

FIGS. 18A-20 are cross section side views of a part of a spatial lightmodulator illustrating one method for fabricating a plurality of torsionhinges and its supports on the support frame.

FIGS. 21-23 are cross section side views of a part of a spatial lightmodulator illustrating one method for fabricating a mirror plate with aplurality of hidden hinges.

FIGS. 24-26 are cross section side views of a part of a spatial lightmodulator illustrating one method for forming the reflective mirrors andreleasing individual mirrors of a micro mirror array.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

A high contrast spatial light modulator (SLM) for display and printingis fabricated by coupling a high active reflection area fill-ratio andnon-diffractive micro mirror array with a high electrostatic efficiencyand low surface adhesion control substrate. A cross section view of apart of the spatial light modulator according to one embodiment of thepresent invention is shown in FIG. 1 a, as the directional light 411 ofillumination 401 at an angle of incidence θi is deflected 412 at anangle of θo toward normal direction of a micro mirror array. In adigital operation mode, this configuration is commonly called the “on”position. FIG. 1 b shows a cross section view of the same part of thespatial light modulator while the mirror plate is rotated toward anotherelectrode under the other side of the hinge 106. The same directionallight 411 is deflected to 412 a much larger angles θi and θopredetermined by the dimensions of mirror plate 102 and the air gapspacing between its lower surfaces of mirror 103 to the landing tips222, and exits toward a light absorber 402.

According to another embodiment of the present invention, the highcontrast SLM is consisted of three major portions: the bottom portion ofcontrol circuitry, the middle portion of a plurality of step electrodes,micro landing tips, hinge support posts, and the upper portion coveredwith a plurality of mirrors with hidden torsion hinges and cavities.

The bottom portion is a wafer substrate 300 with addressing circuitriesto selectively control the operation of each mirror in the micro mirrorarray of SLM. The addressing circuitries comprise array of memory cellsand word-line/bit-line interconnect for communication signals. Theelectrical addressing circuitry on a silicon wafer substrate may befabricated using standard CMOS technology, and resembles a low-densitymemory array.

The middle portion of the high contrast SLM is formed by arrays of stepelectrodes 221, landing tips 222, hinge support posts 105, and a supportframe 202. The multi-level step electrodes 221 in present invention aredesigned to improve the capacitive coupling efficiency of electrostatictorques during the angular cross over transition. By raising theelectrode 221 surfaces near the hinge 106 area, the air gap spacingbetween the mirror plate 103 and the electrodes 221 is effectivelynarrowed. Since the electrostatic attractive force is inverselyproportional to the square of the distance between the mirrors andelectrodes, this effect becomes apparent when mirror is tilted at itslanding positions. When operating in analog mode, high efficientelectrostatic coupling allows a more precise and stable control of thetilting angles of the individual micro mirror in the spatial lightmodulator. In a digital mode, it requires much lower driving voltagepotential in addressing circuitry to operate. The height differencesbetween the first level electrodes 221 to the second may vary from 0.2microns to 3 microns depends on the relative height of air gap betweenthe first level electrodes to the mirror plate.

On the surfaces of control substrate, a pair of stationary verticallanding tips 222 a and 222 b is designed to have same height as that ofsecond level electrodes 221 for manufacturing simplicity. A pair ofstationary vertical tips 222 a and 222 b has two functions. The verticalmicro tips provide a gentle mechanical touch-down for the mirror to landon each angular cross over transition at a pre-determined angleprecisely. Adding a stationary landing tip 222 on the surface of controlsubstrate enhances the robotics of operation and prolongs thereliability of the devices. The second function of these verticallanding tips 222 is providing a mechanism to allow an ease of separationbetween the mirror 103 and its contact stop 222, which effectivelyeliminates the contact surface adhesion during a digital operation ofSLM. For example, to initiate an angular cross over transition, a sharpbipolar pulse voltage Vb is applied on the bias electrode 303, typicallyconnected to each mirror plate 103 through its torsion hinges 106 andsupport posts 105. The voltage potential established by the bipolar biasVb enhances the electrostatic forces on both side of the hinge 106. Thisstrengthening is unequal on two sides at the landing position, due tothe large difference in air gap spacing. Though the increases of biasvoltages Vb on the lower surface of mirror plate 103 a and 103 b hasless impact on which direction the mirror 102 will rotate toward, asharp increase of electrostatic forces F on the whole mirror plate 102provides a dynamic excitation by converting the electromechanicalkinetic energy into an elastic strain energy stored in the deformedmirror hinges 106 and deformed micro landing tips 222 a or 222 b. Aftera bipolar pulse is released on the common bias Vb, the elastic strainenergy of deformed landing tip 222 a or 222 b and deformed mirror hinges106 is converted back to the kinetic energy of mirror plate as itsprings and bounces away from the landing tip 222 a or 222 b. Thisperturbation of mirror plate toward the quiescent state enables a muchsmaller address voltage potential Va for angular cross over transitionof mirror plate 103 from one state to the other.

Hinge support frame 202 on the surface of control substrate 300 isdesigned to strengthen the mechanical stability of the pairs of mirrorsupport posts 105, and retained the electrostatic potentials locally.For the simplicity, the height of support frames 202 is designed to bethe same as the first level electrodes 221. With a fixed size of mirrorplate 103, the height of a pair of hinge support posts 105 willdetermine the maximum deflection angles θ of a micro mirror array.

The upper portion of the high contrast SLM is fully covered by arrays ofmicro mirrors with a flat optically reflective layer 102 on the uppersurfaces and a pair of torsion hinges 106 under the cavities in thelower portion of mirror plate 103. Pair of torsion hinges 106 in themirror plate 103 is fabricated to be part of the mirror plate 103 andare kept in a minimum distance under the reflective surface to allowonly a gap for a pre-determined angular rotation. By minimizing thedistances between a hinge rotating axes 106 to the upper reflectivesurfaces 102, the spatial light modulator effectively eliminates thehorizontal displacement of each mirror during an angular transition.According to the present invention, the gaps between adjacent mirrors inthe array of SLM can be reduced to less than 0.2 microns to achieve thehighest active reflection area fill-ratio of a micro mirror array at thepresent time.

The materials used for micro deflection devices are preferablyconductive, stable, with suitable hardness, elasticity, and stress.Ideally a single material, such as the electromechanical materials, willcover both the stiffness of mirror plate 103 and plasticity of torsionhinges 106 having sufficient strength to deflect without fracturing.Furthermore, all the materials used in constructing the micro mirrorarray have to be processed under 400° C., a typical manufacturingprocess temperature without damaging the pre-fabricated circuitries inthe control substrate.

In the implementation shown in FIGS. 1 a and 1 b, the mirror plate 102includes three layers. A reflective top layer 103 a is made of aluminumand is typically 600 angstrom thick. A middle layer 103 b made of asilicon based material, for example, amorphous silicon, and is typically2000 to 5000 angstrom thick. A bottom layer 103 c is made of titaniumand is typically 600 angstrom thick. As can be seen from FIGS. 1 a and 1b, the hinge 106 can be implemented as part of the bottom layer 103 c.The mirror plate 102 can be fabricated as described below.

According to another embodiment of the present invention, the materialsof mirror plates 103, torsion hinges 106, and support posts 105 are madeof aluminum-silicon based electromechanical materials, such as aluminum,silicon, polysilicon, amorphous silicon, and aluminum-silicon alloys,and their alloys. The deposition is accomplished by PVD magnetronsputtering a single target containing either or both aluminum andsilicon in a controlled chamber with temperature bellow 500° C. Samestructure layers may also be formed by PECVD.

According to another embodiment of the present invention, the materialsof mirror plates 103, torsion hinges 106, and support posts 105 are madeof refractory-metals based electromechanical materials, such astitanium, tantalum, tungsten, molybdenum, their silicides, and theiralloys. Refractory metal and their silicides are compatible with CMOSsemiconductor processing and have relatively good mechanical properties.These materials can be deposited by PVD, by CVD, and by PECVD. Theoptical reflectivity may be enhanced by further PVD depositing a layerof metallic thin-films 102, such as aluminum, gold, or their alloysdepending on the applications on the surfaces of mirror plate 103.

To achieve high contrast ratio of the deflected video images, anyscattered light from a micro mirror array should be reduced oreliminated. Most common interferences come from the diffraction patternsgenerated by the scattering of illumination from the leading andtrailing edges of individual mirrors. The solution to the diffractionproblem is to Weaken the intensity of diffraction pattern and to directthe scattered light from the inactive area of each pixel to differentdirections away from the projection pupil. One method is directing theincident light 411 45° to the edges of the square shape mirror 102pixels, which sometimes called diagonal hinge or diagonal illuminationconfiguration. FIG. 2 is a perspective view showing the top of a part ofthe mirror array with each mirror 102 having a square shape using adiagonal illumination system. The hinges 106 of mirror in the array arefabricated in diagonal direction along two opposite corners of themirror and in perpendicular to the light of illumination 411. Theadvantage of a square shape mirror with a diagonal hinge axis is itsability to deflect the scattered light from the leading and trailingedges 45° away from the projection pupil 403. The disadvantage is thatit requires the projection prism assembly system to be tilted to theedge of the SLM. The diagonal illumination has a low optical couplingefficiency when a conventional rectangular TIR prism system is used toseparate the “on” and “off” light selected by each mirror 102. Thetwisted focusing spot requires an illumination larger than the size ofrectangular micro mirror array surfaces in order to cover all activepixel arrays. A larger rectangular TIR prism increases the cost, size,and the weight of the projection display.

A perspective view of the top of a part of the control circuitrysubstrate for the projection system with diagonal illuminationconfiguration is shown in FIG. 3. The pair of step electrodes 221 isarranged diagonal accordingly to improve the electrostatic efficiency ofthe capacitive coupling to the mirror plate 103. The two micro tips 211a and 211 b act as the landing stops for a mechanical landing of mirrors103 to ensure the precision of tilted angle θ and to overcome thecontact stictions. Made of high spring constant materials, these microtips 222 a and 222 b act as landing springs to reduce the contact areawhen mirrors are snap down. Second function of these micro tips 222 atthe edge of two-level step electrodes 221 is their spring effect toseparate itself from the mirror plates 103. When a sharp bipolar pulsevoltage potential Vb is applied on the mirror 103 through a common bias303 of mirror array, a sharp increase of electrostatic forces F on thewhole mirror plate 103 provides a dynamic excitation by converting theelectromechanical kinetic energy into an elastic strain energy stored inthe deformed mirror hinges 106. The elastic strain energy is convertedback to the kinetic energy of mirror plate 103 as it springs and bouncesaway from the landing tip 222.

The periodic array of the straight or corner shape edges of mirror in aSLM creates a diffraction patterns tended to reduce the contrast ofprojected images by scattering the illumination 411 at a fixed angle. Acurvature shape leading and trailing edges of mirror in the arraygenerates much weaker diffraction patterns due to the variation ofscattering angles of the illumination 411 on the edges of mirror.According to another embodiment of the present invention, the reductionof the diffraction intensity into the projection pupil 403 while stillmaintaining an orthogonal illumination optics system is achieved byreplacing the straight or fixed angular corner shape edges of arectangular shape mirror with at least one or a series curvature shapeleading and trailing edges with opposite recesses and extensions.Forming a curvature in the leading and trailing edges that is inperpendicular to the incident illumination 411 weakens the diffractionintensity and reduces a large portion of scattering light diffracteddirectly into the projection system.

Orthogonal illumination has a higher optical system coupling efficiency,and requires a less expensive, smaller size, and lighter TIR prism.However, since the scattered light from both leading and trailing edgesof mirror is scattered straightly into the projection pupil 403, itcreates a diffraction patterns reducing the contrast ratio of a SLM.FIG. 4 shows a perspective view of the top of a part of mirror arraywith rectangular shape mirrors for the projection system with orthogonalillumination configuration. The torsion hinges 106 are in parallel tothe leading and trailing edges of mirror and in perpendicular to thelight of illumination 411. So the mirror pixels in the SLM areilluminated orthogonally. In FIG. 4, each mirror in the array has aseries of curvatures in the leading edge extension and trailing edgerecession. The principle is that a curvature edge weakens thediffraction intensity of scattered light and it further diffracts alarge portion of scattered light at a variation of angles away from theoptical projection pupil 403. The radius curvature of leading andtrailing edges of each mirror r may vary depending on the numbers ofcurvatures selected. As the radius of curvature r becomes smaller, thediffraction reduction effect becomes more prominent. To maximize thediffraction reduction effects, according to another embodiment of thepresent invention, a series of small radius curvatures r are designed toform the leading and trailing edges of each mirror in the array. Thenumber of curvatures may vary depending on the size of mirror pixels,with a 10 microns size square mirror pixel, two to four curvatures oneach leading and trailing edges provides an optimum results an lowdiffraction and within current manufacturing capability.

FIG. 5 is a perspective view showing the top of a part of the controlcircuitry substrate 300 for a projection system with orthogonalillumination 411 configurations. Unlike conventional flat electrodes,the two-level step electrodes 221 raised above the surface of controlsubstrate 300 near the hinge axis narrows the effective air gap spacingbetween the flat mirror plate 103 and the bottom electrodes 221, whichsignificantly enhancing the electrostatic efficiency of capacitivecoupling of mirror plate 103. The number of levels for the stepelectrodes 221 can be varying from one to ten. However, the larger thenumber of levels for step electrodes 221 the more complicated and costlyit takes to manufacture the devices. A more practical number would befrom two to three. FIG. 5 also shows the mechanical landing stops madeof micro tips 222 oriented in perpendicular to the surface of controlsubstrate 300. These tips 222 provide a mechanical stop during thelanding operation of angular cross over transitions. The micro tips 222at the edge of step electrodes 221 act as landing tips to furtherovercome the contact surface adhesion. This low voltage driven and highefficiency micro mirror array design allows an operation of a largertotal deflection angle (|θ|>15°) of micro mirrors to enhance thebrightness and contrast ratio of the SLM.

Another advantage of this reflective spatial light modulator is that itproduces the highest possible active reflection area fill-ratio bypositioning the torsion hinge 106 under the cavities in the lowerportion of mirror plate 103, which almost completely eliminates thehorizontal displacement of mirror 103 during an angular cross overtransition. An enlarged backside view of a part of the mirror arraydesigned to reduce diffraction intensity using four-curvature leadingand trailing edges is shown in FIG. 6 for a projection system withorthogonal illumination 411 configuration. Again, pairs of torsionhinges 106 are positioned under two cavities as part of the mirror lowerportion 103 and supported by a pair of support posts 105 on top ofsupport frames 202. A pair of hinge support post 105 has a width Win thecross section much larger than the width of torsion hinge bar 106. Sincethe distance between the axis of hinge 106 to the reflective surfaces ofmirror is kept minimum, a high active reflection area fill-ratio isachieved by closely packed individual mirror pixels without worrying thehorizontal displacement. In one of the present invention, mirror pixelsize (a×b) is about 10 microns×10 microns, while the radius of curvaturer is about 2.5 microns.

FIG. 7 is an enlarged backside view of a part of the mirror plateshowing the torsion hinges 106 and their support posts 105 under thecavities in the lower portion of a mirror plate 103. To achieve optimumperformance, it is important to maintain a minimum air gap G in thecavity where the torsion hinges 106 are created. The dimension of hinges106 varies depending on the size of the mirrors 102. At presentinvention, the dimension of each torsion hinge 106 is about 0.1×0.2×3.5microns, while the support post 105 has a square shape cross sectionwith each side W about 1.0 micron width. Since the top surfaces ofsupport posts 105 are also under the cavities as lower part of themirror plate 103, the air gap G in the cavity needs to be high enough toaccommodate the angular rotation of mirror plate 103 without touchingthe larger hinge support posts 105 at a predetermined angle 0. In orderfor the mirror to rotate a pre-determined angle θ without touching thehinge support post 105, the air gap of the cavities where torsion hinges106 are positioned must be larger than G=0.5×W×SIN(θ), where W is thecross section width of hinge support posts 105.

FIG. 8 is a diagram illustrates a minimum air gap spacing G around thetorsion hinge 106 of a mirror plate 103 when rotated 15° in onedirection. The calculation indicates the air gap spacing G of torsionhinge 106 in the cavity must be larger than G=0.13 W. If width of eachside W of a square shape hinge support post 105 is 1.0 micron, the airgap spacing G in the cavity should be larger than 0.13 microns. Withouthorizontal displacement during the angular transition operation, thehorizontal gap between the individual mirrors in the micro mirror arraymay be reduced to less than 0.2 microns, which led to a 96% activereflection area fill-ratio of the SLM according to the presentinvention.

According to another embodiment of the present invention, fabrication ofa high contrast spatial light modulator is divided into four sequentialsections using standard CMOS technology. First is forming a controlsilicon wafer substrate with support frames and arrays of first levelelectrodes on the surfaces and connected to the memory cells in theaddressing circuitry in the wafer, resembling a low-density memoryarray. Second is forming a plurality of second level electrodes, microlanding tips, and hinge support posts on the surfaces of controlsubstrate. Third is forming a plurality of mirrors with hidden hinges oneach pairs of support posts. At last, the fabricated wafer is separatedinto individual spatial light modulation device dies before finallyremoving the remaining sacrificial materials.

One preferred embodiments of the manufacturing process flow diagram fora high contrast spatial light modulator is shown in FIG. 9. Themanufacturing processes starts by fabricating a CMOS circuitry waferhaving a plurality of memory cells and word-line/bit-lineinterconnection structures for communicating signals as the controlsubstrate using common semiconductor technology 810. A plurality offirst level electrodes and support frames are formed by patterning aplurality of via through the passivation layer of circuitry opening upthe addressing nodes in the control substrate 820. To enhance theadhesion for subsequent electromechanical layer, the via and contactopenings are exposed to a 2000 watts of RF or microwave plasma with 2torr total pressures of a mixture of O2, CF4, and H2O gases at a ratioof 40:1:5 at about 250° C. temperatures for less than five minutes. Anelectromechanical layer is deposited by physical vapor deposition (PVD)or plasma-enhanced chemical vapor deposition (PECVD) depending on thematerials selected filling via and forming an electrode layer on thesurface of control substrate 821. Then the electromechanical layer ispatterned and etched anisotropically through to form a plurality ofelectrodes and support frames 822. The partially fabricated wafer istested 823 to ensure the electrical functionality before proceeding tofurther processes.

According to one preferred embodiment of the present invention, theelectromechanical layer is aluminum metallization, which can take theform of a pure Al, titanium, tantalum, tungsten, molybdenum film, anAl/poly-Si composite, an Al—Cu alloy, or an Al—Si alloy. While each ofthese metallization has slightly different etching characteristics, theyall can be etched in similar chemistry in plasma etching of Al. Inpresent invention, a two step processes is carried out to etch aluminummetallization layers anisotropically. First, the wafer is etched ininductive coupled plasma while flowing with BCl3, Cl2, and Ar mixturesat flow rates of 100 sccm, 20 sccm, and 20 sccm respectively. Theoperating pressure is in the range of 10 to 50 mTorr, the inductivecoupled plasma bias power is 300 watts, and the source power is 1000watts. During the etching process, wafer is cooled with a backsidehelium gas flow of 20 sccm at a pressure of 1 Torr. Since the Al patterncan not simply be removed from the etching chamber into ambientatmosphere, a second oxygen plasma treatment step must be performed toclean and passivate Al surfaces. In a passivation process, the surfacesof partially fabricated wafer is exposed to a 2000 watts of RF ormicrowave plasma with 2 torr pressures of a 3000 sccm of H2O vapor atabout 250° C. temperatures for less than three minutes.

According to another embodiment of the present invention, theelectromechanical layer is silicon metallization, which can take theform of a polysilicon, a polycides, or a silicide. While each of theseelectromechanical layers has slightly different etching characteristics,they all can be etched in similar chemistry in plasma etching ofpolysilicon. Anisotropic etching of polysilicon can be accomplished withmost Cl and F based feedstock, such as Cl2, BCl3, CF4, NF3, SF6, HBr,and their mixtures with Ar, N2, O2, and H2. In present invention, thepoly silicon or silicide layer (WSix, or TiSix, or TaSi) is etchedanisotropically in inductive decoupled plasma while flowing with Cl2,BCl3, HBr, and HeO2 gases at flow rates of 100 sccm, 50 sccm, sccm, and10 sccm respectively. In another embodiment, the polycide layer isetched anisotropically in a reactive ion etch chamber flowing with Cl2,SF6, HBr, and HeO2 gases at a flow rate of 50 sccm, 40 sccm, 40 sccm,and 10 sccm respectively. In both cases, the operating pressure is inthe range of 10 to 30 mTorr, the inductive coupled plasma bias power is100 watts, and the source power is 1200 watts. During the etchingprocess, wafer is cooled with a backside helium gas flow of 20 sccm at apressure of 1 Torr. A typical etch rate can reach 9000 angstroms perminute.

In order to improve the electrostatic efficiency and reduce the stictionduring the angular cross over transition of the micro mirror arrays, aplurality of second level electrodes and micro landing tips arefabricated on the surfaces of control substrate. First, a layer ofsacrificial materials is deposited with a predetermined thickness on thesurface of partially fabricated wafer 830. If the sacrificial materialis photoresist, the layer is spin coated on the surface. If it isorganic polymer, the layer is deposited by PECVD. To prepare for thesubsequent build up, the sacrificial layer has to be hardened byexposing the layer to ultraviolet light, then exposing to a CF4 plasmafor about three minutes, then baking the layer at about 150° C. forabout two hours, finally exposing the layer to oxygen plasma for aboutone minute. Second, the sacrificial layer is patterned forming via andcontact openings for a plurality of second level electrodes, landingtips, and support posts 831. Third, a second electromechanical layer isdeposited by PVD or PECVD depending on the materials selected forming aplurality of second level electrodes, landing tips, and support posts832. Finally, the second electromechanical layer is planarized to apredetermined thickness by chemical mechanical polishing (CMP) 833. Apreferred height of second level electrodes and micro landing tips isless than one micron.

Once the raised multi-level step electrodes and micro landing tips areformed on the CMOS control circuitry substrate, a plurality of mirrorswith hidden hinges on each pairs of support posts are fabricated. Theprocesses started with depositing sacrificial materials with apredetermined thickness on the surface of partially fabricated wafer840. Then sacrificial layer is patterned to form via for a plurality ofhinge support posts 841. The sacrificial layer is further hardenedbefore a deposition of electromechanical materials by PVD or PECVDdepending on materials selected to fill via and form a thin layer fortorsion hinges and part of mirrors 842. The electromechanical layerplanarized to a predetermined thickness by CMP 843. Theelectromechanical layer is patterned a plurality of openings to form aplurality of torsion hinges 850. To form a plurality of cavities in thelower portion of mirror plate and torsion hinges positioned under thecavity, sacrificial materials is again deposited to fill the openinggaps around the torsion hinges and to form a thin layer with apredetermined thickness on top of hinges 851. A preferred thickness isslightly larger than G=0.5×W×SIN(O), where W is the cross section widthof hinge support posts 105. The sacrificial layer patterned to form aplurality of spacers on top of each torsion hinge 852. Moreelectromechanical materials are deposited to cover the surface ofpartially fabricated wafer 853. The electromechanical layer isplanarized to a predetermined thickness by CMP 854 before patterned aplurality of openings to form a plurality of air gaps between individualmirror plates 870. The reflectivity of mirror surface may be enhanced bya PVD deposition of 400 angstroms or less thickness reflective layerselected from the group consisting of aluminum, gold, and combinationsthereof 860.

To separate the fabricated wafer into individual spatial lightmodulation device dies, a thick layer of sacrificial materials isdeposited to cover the fabricated wafer surfaces for protection 880.Then the fabricated wafer is partially sawed 881 before separating intoindividual dies by scribing and breaking 882. The spatial lightmodulator device die is attached to the chip base with wire bonds andinterconnects 883 before a RF or microwave plasma striping of theremaining sacrificial materials 884. The SLM device die is furtherlubricated by exposing to a PECVD coating of lubricants in theinterfaces between the mirror plate and the surface of electrodes andlanding tips 885 before electro-optical functional test 886. Finally,the SLM device is hermetically sealed with a glass window lip 887 andsent to burn-in process for reliability and robust quality control 888.

One of the major problems in the digital operation of micro mirror arrayis the high stiction of micro mirror at a mechanical landing position.The surface contact adhesion could increases beyond the electrostaticforce of control circuitry causing the device from stiction failure in amoisture environment. To reduce the contact adhesion between the mirrorplate 103 and landing tips 222, and protect the mechanical weardegradation of interfaces during the touch and impact of angular crossover transition, a thin lubricated coating is deposited on the lowerportion of mirror plate 103 and on the surface of electrodes 221 andlanding tips 222. The lubricants chosen should be thermally stable, lowvapor pressure, and non-reactive with metallization andelectromechanical materials that formed the micro mirror array devices.

In the embodiment of the presentation invention, fluorocarbon thin filmis coated to the surfaces of the lower portion of mirror plate and onthe surface of electrodes and landing tips. The SLM device die isexposed to plasma of fluorocarbons, such as CF4, at a substratetemperature of about 200° C. temperatures for less than five minutes.The fluorine on the surfaces 103 serves to prevent adherence orattachment of water to the interfaces of mirror plate and the underneathelectrodes and landing tips, which eliminates the impact of humidity inthe stiction of mirror during landing operation. Coating fluorocarbonfilm in the interfaces between the mirror plate 103 and underneathelectrodes 221 and landing tips 222 provides a sufficient repellentperformance to water due to the fluorine atoms existing near the exposedsurfaces.

In another embodiment of present invention, a perfluoropolyether (PFPE)or a mixture of PFPE or a phosphazine derivative is deposited by PECVDin the interfaces between the mirror plate 103 and underneath electrodes221 and landing tips 222 at a substrate temperature of about 200° C.temperatures for less than five minutes. PFPE molecules have anaggregate vapor pressure in the range of 1×10⁻⁶ to 1×10⁻¹¹ atm. Thethickness of lubricant film is less than 1000 angstroms. To improve theadhesion and lubricating performance on the surface of a metallizationor an electromechanical layer, phosphate esters may be chosen because ofits affinity with the metallic surface.

More detail description of each process to fabricate a high contrastspatial light modulator is illustrated in a series of cross sectiondiagrams. FIG. 10 to FIG. 13 are cross section side views of a part of aspatial light modulator illustrating one method for fabricating aplurality of support frames and the first level electrodes connected tothe memory cells in the addressing circuitry. FIG. 14 to FIG. 17 arecross section side views of a part of a spatial light modulatorillustrating one method for fabricating a plurality of support posts,second level electrodes, and landing tips on the surface of controlsubstrate. FIG. 18 to FIG. 20 are cross section side views of a part ofa spatial light modulator illustrating one method for fabricating aplurality of torsion hinges and its supports on the support frame. FIG.21 to FIG. 23 are cross section side views of a part of a spatial lightmodulator illustrating one method for fabricating a mirror plate with aplurality of hidden hinges. FIG. 23 to FIG. 26 are cross section sideviews of a part of a spatial light modulator illustrating one method forforming the reflective mirrors and releasing individual mirrors of amicro mirror array.

FIG. 10 is a cross sectional view that illustrates the control siliconwafer substrate 600 after using standard CMOS fabrication technology. Inone embodiment, the control circuitry in the control substrate includesan array of memory cells, and word-line/bit-line interconnects forcommunication signals. There are many different methods to makeelectrical circuitry that performs the addressing function. The DRAM,SRAM, and latch devices commonly known may all perform the addressingfunction. Since the mirror plate 102 area may be relatively large onsemiconductor scales (for example, the mirror plate 102 may have an areaof larger then 100 square microns), complex circuitry can bemanufactured beneath micro mirror 102. Possible circuitry includes, butis not limited to, storage buffers to store time sequential pixelinformation, and circuitry to perform pulse width modulationconversions.

In a typical CMOS fabrication process, the control silicon wafersubstrate is covered with a passivation layer 601 such as silicon oxideor silicon nitride. The passivated control substrate 600 is patternedand etched anisotropically to form via 621 connected to theword-line/bit-line interconnects in the addressing circuitry, shown inFIG. 11. According to another embodiment of the present invention,anisotropic etching of dielectric materials, such silicon oxides orsilicon nitrides, is accomplished with C2F6 and CHF3 based feedstock andtheir mixtures with He and O2. One preferred high selectivity dielectricetching process flows C2F6, CHF3, He, and O2 at a ratio of 10:10:5:2mixtures at a total pressure of 100 mTorr with inductive source power of1200 watts and a bias power 600 watts. The wafers are then cooled with abackside helium gas flow of 20 sccm at a pressure of 2 torr. A typicalsilicon oxides etch rate can reach 8000 angstroms per minute.

Next, FIG. 12 shows that an electromechanical layer 602 is deposited byPVD or PECVD depending on the electromechanical materials selected. Thiselectromechanical layer 602 is patterned to define hinge support frames202 and the first level electrodes 221 corresponding to each micromirror 102, shown in FIG. 12. The patterning electromechanical layer 602is performed by the following processes. First, a layer of photoresistis spin coated to cover the substrate surface. Then photoresist layer isexposed to standard photolithography and developed to form predeterminedpatterns. The electromechanical layer is etched anisotropically throughto form a plurality of via and openings. Once via and openings areformed, the partially fabricated wafer is cleaned by removing theresidues from the surfaces and inside the openings. This is accomplishedby exposing the patterned wafer to a 2000 watts of RF or microwaveplasma with 2 torr total pressures of a mixture of O2, CF4, and H2Ogases at a ratio of 40:1:5 at about 250° C. temperatures for less thanfive minutes. Finally, the surfaces of electromechanical layer ispassivated by exposing to a 2000 watts of RF or microwave plasma with 2torr pressures of a 3000 sccm of H2O vapor at about 250° C. temperaturesfor less than three minutes.

Next step is forming a plurality of second level electrodes 221, microlanding tips 222, and support pots 105 on the surface of partiallyfabricated wafer. A micron thick sacrificial material 604 is depositedon the substrate surface, which can be spin coated photoresist or PECVDof organic polymers, shown in FIG. 13. The sacrificial layer 604 ishardened by a series thermal and plasma treatments to transformstructure of materials from a hydrophobic state to hydrophilic state ofpolymers. First, the sacrificial layer 604 is exposed to ultravioletlight, then to a CF4 plasma for about three minutes, followed by bakingsacrificial layer at about 150° C. for about two hours before exposingsacrificial layer to oxygen plasma for about one minute. In some case,implanting the sacrificial layer with KeV energy of silicon, boron, orphosphors ions further hardens the sacrificial layers 604.

Then, sacrificial layer 604 is patterned to form a plurality of via andcontact openings for second level electrodes 632, micro landing tips633, and support pots 631 as shown in FIG. 15. The openings 633 for thelanding tips can be etched into the electromechanical layer 602 so thatthe landing tips can be formed anchoring into the substrate as shown inFIGS. 16-26. Similarly, the opening 631 for the support post can also beetched into the substrate layer to allow electromechanical material 603to be filled to form a support post having a protrusion anchored in thesubstrate (in this context, the substrate can be considered to includethe electromechanical layer 602). In another implementation, the openingcan extend entirely through the electromechanical layer 602 and into thesubstrate 600 itself. In another implementation, the electromechanicallayer 602 is absent, and the opening 631 is formed directly in thesubstrate 600.

To enhance the adhesion for subsequent electromechanical layer, the viaand contact openings are exposed to a 2000 watts of RF or microwaveplasma with 2 torr total pressures of a mixture of O2, CF4, and H2Ogases at a ratio of 40:1:5 at about 250° C. temperatures for less thanfive minutes. Electromechanical material 603 is then deposited to fillvia and contact openings as well as the etched recess area at the baseof the landing tips. As a result the landing tips are anchored in thesubstrate (i.e. the electromechanical layer 602). By providing anchoringin the substrate, the landing tips can be more strongly rooted into thesubstrate which allows the landing tips to sustain repeated impact fromstopping the rotating mirror plates in light-modulation operations. Thelower portion of the landing tips are anchored or buried in thesubstrate. The lower portion of the landing tip can take a tapered shapeor can have substantially the same width as the upper portion of thelanding tip.

The filling is done by either PECVD or PVD depending on the materialsselected. For the materials selected from the group consisting ofaluminum, titanium, tungsten, molybdenum, their alloys, PVD is a commondeposition method in the semiconductor industry. For the materialsselected from the group consisting of silicon, polysilicon, silicide,polycide, tungsten, their combinations, PECVD is chosen as a method ofdeposition. The partially fabricated wafer is further planarized by CMPto a predetermined thickness slightly less than one micron shown in FIG.16.

After the CMP planarization, FIG. 17 shows that another layer ofsacrificial materials 604 is spin coated on the blanket surface to apredetermined thickness and hardened to form the air gap spacer underthe torsion hinges. The sacrificial layer 604 is patterned to form aplurality of via or contact openings for hinge support posts 641 asshown in FIGS. 18A and 18B. A recess region 638 is etched in the topsurface of the hinge support post. In FIG. 19, electromechanicalmaterial is deposited to fill via and form a torsion hinge layer 605 onthe surface. This hinge layer 605 is then planarized by CMP to apredetermined thickness. The thickness of electromechanical layer 605formed here defines the thickness of torsion hinge bar and themechanical performance of mirror later on. The partially fabricatedwafer is patterned and etched anisotropically to form a plurality oftorsion hinges 106 in the electromechanical layers 605 as shown in FIG.20. As shown in FIG. 20, the torsion hinge 106 includes a protrusion 639that is anchored in the recess region 638 over the top of the hingesupport post. The protrusion 639 strengthens the connection between thetorsion hinge 106 and the hinge support post. Durability and reliabilityof the micro mirror device are significantly increased as a result. Asshown in FIGS. 18A through FIG. 26, the hinge support post may includemultiple portions stacked up over each other. Each portion can be lockedinto the portion below by a anchor-hole mechanism as described above.

In summary, the landing tip or the hinge support post can be is formedanchored in the substrate by the following steps: forming a hole in theupper surface of the substrate, depositing a layer of material over theupper surface of the substrate and in the hole of the substrate,selectively removing the deposited or other sacrificial materials overthe substrate so that the remainder material will form the upper portionof the landing tip and the hinge support post, and removing or polishingdeposited material to flatten the top surface of the material depositedover the substrate. The landing tips and the hinge support posts formedas a result can be substantially upright relative to the substrate.

More sacrificial materials 604 is deposited to fill the openings 643surrounding each hinges and to form a thin layer 604 with predeterminedthickness on the surface, as shown in FIG. 21. The thickness of thislayer 604 defines the height of the spacers on top of each torsionhinges 106. The sacrificial layer 604 is then patterned to form aplurality of spacers on top of each torsion hinges 106, as shown in FIG.22. Since the top surfaces of support posts 642 are also under thecavities as lower part of the mirror plate 103, the air gap G in thecavity needs to be high enough to accommodate the angular rotation ofmirror plate 103 without touching the larger hinge support posts 105 ata pre-determined angle θ. In order for the mirror to rotate apre-determined angle θ without touching the hinge support post 105, theair gap of the cavities where torsion hinges 106 are positioned must belarger than G=0.5×W×SIN(θ), where W is the cross section width of hingesupport posts 105. In the present invention, each mirror in the arraymay rotate 15° in each direction. The calculation indicates the air gapspacing G of torsion hinge 106 in the cavity must be larger than G=0.13W. If width of each side W of a square shape hinge support post 105 is1.0 micron, the air gap spacing G in the cavity should be larger than0.13 microns.

To form a mirror with torsion hinges 106 under each cavities in thelower portion of mirror plate 103, more electromechanical materials 605is deposited to cover a plurality of sacrificial spacers, as shown inFIG. 23. In some cases, a chemical-mechanical-polished (CMP) process isadded to ensure a flat reflective surface of electromechanical layer 605has been achieved before etching to form individual mirrors. Thethickness of the total electromechanical layer 605 will ultimately bethe approximate thickness of the mirror plate 103 eventually fabricated.In FIG. 23, surface of partially fabricated wafer is planarized by CMPto a predetermined thickness of mirror plate 103. In present invention,the thickness of mirror plate 605 is between 0.3 microns to 0.5 microns.If the electromechanical material is aluminum or its metallic alloy, thereflectivity of mirror is high enough for most of display applications.For some other electromechanical materials or for other applications,reflectivity of mirror surface may be enhanced by deposition of areflective layer 606 of 400 angstroms or less thickness selected fromthe group consisting of aluminum, gold, their alloys, and combinations,as shown in FIG. 24. The reflective surface 606 of electromechanicallayer is then patterned and etched anisotropically through to form aplurality of individual mirrors, as shown in FIG. 25.

FIG. 26 shows the remaining sacrificial materials 604 are removed andresidues are cleaned through a plurality of air gaps between eachindividual mirrors in the array to form a functional micro mirror arraybased spatial light modulator. In a real manufacturing environment, moreprocesses are required before delivering a functional spatial lightmodulator for video display application. After reflective surface 606 ofelectromechanical layer 605 is patterned and etched anisotropicallythrough to form a plurality of individual mirrors, more sacrificialmaterials 604 are deposited to cover the surface of fabricated wafer.With its surface protected by a layer of sacrificial layer 604,fabricated wafer is going through common semiconductor packagingprocesses to form individual device dies. In a packaging process,fabricated wafer is partially sawed 881 before separating intoindividual dies by scribing and breaking 882. The spatial lightmodulator device die is attached to the chip base with wire bonds andinterconnects 883 before striping the remaining sacrificial materials604 and its residues in the structures 884. The cleaning is accomplishedby exposing the patterned wafer to 2000 watts of RF or microwave plasmawith 2 torr total pressures of a mixture of O2, CF4, and H2O gases at aratio of 40:1:5 at about 250° C. temperatures for less than fiveminutes. Finally, the surfaces of electromechanical and metallizationstructures are passivated by exposing to a 2000 watts of RF or microwaveplasma with 2 torr pressures of a 3000 sccm of H₂O vapor at about 250°C. temperatures for less than three minutes.

The SLM device die is further coated a anti-stiction layer inside theopening structures by exposing to a PECVD of fluorocarbon at about 200°C. temperatures for less than five minutes 885 before plasma cleaningand electro-optical functional test 886. Finally, the SLM device ishermetically sealed with a glass window lip 887 and sent to burn-inprocess for reliability and robust quality control 888.

Although the invention has been particularly shown and described withreference to multiple embodiments, it will be understood by personsskilled in the relevant art that various changes in form and details canbe made therein without departing from the spirit and scope of theinvention. For example, the same 3-dimensional multi-layer structuresmay be constructed by patterning and etching the electromechanicallayers, rather than patterning the sacrificial layers and etching via.Furthermore, the disclosed SLM device can include a single landing tipjoined to the substrate for stopping the rotation of a mirror plate. Asdescribed above, the mirror plate can be rotated by an electrostaticforce toward the landing tip. The landing tip can come to contact withthe lower surface of the mirror plate to stop its rotation. Theorientation of the mirror plate when it is in contact with the landingtip defines one angular position of the mirror plate for lightmodulation. The contact between the landing tip and the mirror platestores an elastic energy in the bent landing tip. The mirror plate canbe rotated away from the landing tip by another electrostatic force. Therelease of the elastic force from the bent landing tip helps to overcomethe contact stiction between the landing tip and the mirror plate. Themirror plate can be tilted to the horizontal direction or anotherangular direction, which defines a second state of light modulation bythe mirror plate.

1. A spatial light modulator, comprising: a mirror plate comprising areflective upper surface, a lower surface, and a substrate portioncomprising a cavity having an opening on the lower surface; a substratecomprising an upper surface, a hinge support post in connection with thesubstrate, and a hinge component supported by the hinge support post andin connection with the mirror plate, wherein the hinge componentincludes a protrusion that is anchored in a hole in the top surface ofthe hinge support post and the hinge component is configured to extendinto the cavity to facilitate rotation of the mirror plate; and one ormore landing tips configured to contact the lower surface of the mirrorplate to limit rotation of the mirror plate.
 2. The spatial lightmodulator of claim 1, wherein at least one of the landing tips isanchored into the upper surface of the substrate.
 3. The spatial lightmodulator of claim 1, wherein the protrusion and the hinge componentcomprise a unitary body.
 4. The spatial light modulator of claim 1,wherein the hinge support post is substantially upright.
 5. The spatiallight modulator of claim 1, wherein the hinge support post is anchoredinto the upper surface of the substrate.
 6. The spatial light modulatorof claim 1, wherein the one or more landing tips or the one or more ofthe hinge support posts comprise a material selected from the groupconsisting of aluminum, silicon, amorphous silicon, and analuminum-silicon alloy.
 7. The spatial light modulator of claim 1,wherein the cavity in the substrate portion of the mirror plate and theassociated hinge component are so configured such that a gap is formedbetween the hinge component and the surfaces in the cavity to permit therotation of the mirror plate.
 8. The spatial light modulator of claim 1,wherein the hinge support post over the upper surface is substantiallyupright relative to the substrate.
 9. A spatial light modulator,comprising: a mirror plate comprising a reflective upper surface, alower surface, and a substrate portion comprising a cavity havingopenings on the lower surface; a substrate comprising an upper surface,a hinge support post in connection with the upper surface, and a hingecomponents supported by the hinge support post and in connection withthe mirror plate, wherein the hinge component is configured to extendinto the cavity to facilitate a rotation of the mirror plate; and one ormore landing tips anchored into the upper surface of the substrate,configured to contact the lower surface of the mirror plate to limit therotation of the mirror plate.
 10. The spatial light modulator of claim9, wherein the hinge component includes a protrusion that is anchored ina hole in the top surface of the hinge support post.
 11. The spatiallight modulator of claim 9, wherein the hinge support post is anchoredinto the upper surface of the substrate.
 12. The spatial light modulatorof claim 9, wherein at least one of the landing tips includes a lowerportion anchored in the upper surface of the substrate and an upperportion above the substrate.
 13. The spatial light modulator of claim12, wherein the lower portion of the at least one of the landing tipsincludes a tapered shape anchored in the upper surface of the substrate.14. The spatial light modulator of claim 12, wherein the lower portionof the at least one of the landing tips has substantially the same widthas the upper portion of the landing tip.
 15. The spatial light modulatorof claim 1, wherein the substrate includes a hinge support layer intowhich the landing tip is anchored.
 16. The spatial light modulator ofclaim 1, wherein the top surface of the landing tip is substantiallyflat.
 17. The spatial light modulator of claim 1, wherein the one ormore landing tips are configured to stop the rotation of the mirrorplate when the mirror plate is rotated to one or more predeterminedorientations.
 18. The spatial light modulator of claim 1, wherein theone or more landing tips are substantially upright when the landing tipsare not in contact with the lower surface of the mirror plate.
 19. Aspatial light modulator, comprising: a mirror plate comprising areflective upper surface, a lower surface having a conductive surfaceportion, and a substrate portion comprising one or more cavities havingopenings on the lower surface; a control substrate comprising an uppersurface, one or more electrodes over the upper surface, one or morehinge support post in connection with the upper surface, and one or morehinge components each supported by one of the hinge support posts,wherein at least one of the hinge components includes a protrusion thatis anchored in a hole in the top surface of the hinge support post andthe hinge component is configured to extend into one of the cavities tofacilitate a rotation of the mirror plate when an electric voltage isapplied across one of the electrodes over the control substrate and theconductive surface portion in the lower surface of the mirror plate; andone or more landing tips anchored into the upper surface of the controlsubstrate, configured to contact the lower surface of the mirror plateto limit the rotation of the mirror plate.
 20. A method for fabricatinga landing tip for stopping the rotation of a mirror plate hinged to ahinge support post in connection with a substrate, comprising: forming ahole in the upper surface of the substrate; depositing a layer ofmaterial over the upper surface of the substrate and in the hole of thesubstrate, wherein the lower portion of the landing tip is to be formedby the material deposited in the hole; and selectively removing thedeposited material over the substrate to form the upper portion of thelanding tip.
 21. The spatial light modulator of claim 20, furthercomprising: removing deposited material to flatten the top surface ofthe material deposited over the substrate.
 22. A method for fabricatinga hinge component in connection with a mirror plate and a hinge supportpost to facilitate the rotation of the mirror plate relative to thehinge support post, comprising: forming a hole in the top surface of thehinge support post; depositing a layer of material over the top surfaceof the hinge support post and in the hole in the top surface of thehinge support post; and selectively removing the deposited material overthe substrate to form the hinge component having the protrusion anchoredin the hole in the top surface of the hinge support post.
 23. A methodfor fabricating a hinge support post in connection with a mirror plateand a substrate to facilitate the rotation of the mirror plate relativeto the substrate, comprising: forming a hole in the upper surface of thesubstrate; depositing a layer of material over the upper surface of thesubstrate and in the hole of the substrate, wherein the lower portion ofthe landing tip is to be formed by the material deposited in the hole;and selectively removing the deposited material over the substrate toform the upper portion of the hinge support post.
 24. The spatial lightmodulator of claim 23, further comprising: removing deposited materialto flatten the top surface of the material deposited over the substrate.